Selection of the Appropriate Mechanical Face Seal
Cast in Ni-Hard
As a result of very high requirements for the wear resistance of mechanical face seals we make use of a special cast with a natural hardness of 58 to 64 HRC, which consists of a material called Ni-Hard. The extremely high wear resistance is reached by a carbidic-martensite structure of the material and a selection of the alloy elements as well as their concentration. By means of the combination of selected alloy elements and the high carbon content a structural composition is achieved, which proves to be advantageous with respect to wear resistance compared to other materials such as steel. At the same time this material performs with a low corrosion index.
Peripheral Speeds
Mechanical face seals in high alloy cast allow peripheral speeds up to 10 m/s with oil- and up to 3 m/s with grease lubrication, while mechanical face seals in bearing steel (100CR6) can be used with rotary speeds up to 2 m/s.
Individual Material Recipes
Depending on the media to be sealed off, it is possible to compile individual material recipes for a special high alloy cast in order to substantially increase life span and wear resistance of the mechanical face seal.
Selection of O-ring Material
High thermal resistance and a low compression set are the essential criteria specified for the elastomeric material in demanding applications. The standard design NBR meets these requirements with the use of nitrile-butadiene-rubber. For higher thermal stresses the O-rings are constructed of HNBR, VMQ or FKM. The oil compatibility of several elastomers has to be examined. The elastomeric materials listed are offered in various degrees of hardness (ShoreA), so that the O-ring can adequately perform its function of generating a permanent and consistent contact pressure within the sealing system.
NBR - Nitrile-Butadiene-Rubber
Nitrile is recommended for temperatures ranging from -35 °C to 100 °C (-95 °F to 212 °F) continuous and is compatible with most mineral based lubricant oils. Nitrile O-rings offer the maximum resistance to abrasion. It is the most common O-ring material choice and is used in most standard axle, final drive and undercarriage applications.
HNBR - Hydrogenated Nitrile-Butadiene-Rubber
HNBR is a nitrile-based material recommended for temperatures ranging from -40 °C to 135 °C (-104 °F to 275 °F) continuous. It has very similar abrasion resistance characteristics to standard nitrile, but HNBR has better resistance to compression sets (permanent deformations) when exposed to high temperatures for extended periods of time.
VMQ - Silicone-Rubber
Silicone is recommended for temperatures ranging from -55 °C to 200 °C (-131 °F to 392 °F) continuous. It is not compatible with fuels or certain types of gear lubricants. Silicone also has inferior abrasion resistance to nitrile. Typically, silicone uses are: extreme high (wet disc brake systems) or extreme low (arctic environment) temperature applications.
FKM – Fluorocarbon-Rubber
FKM has a recommended temperature range between -10 °C to 180 °C (-50 °F to 356 °F). FKM is typically used in steel mill type applications where extremely high temperatures are a concern and low temperatures are not a problem. FKM has a very weak low temperature capability and will harden at temperatures near freezing.